President Rodrigo Duterte has increased the bounties for top militant leaders Isnilon Hapilon and the Maute brothers, with a total of 27.4m pesos now offered for their "neutralisation". The US is offering a separate $5m bounty for Hapilon.

The US is supplying weapons, including machine guns and grenade launchers, to the Philippines which has said they will go to soldiers fighting in Marawi.

The militants were also apparently well-prepared for a possible siege, and had placed supplies in mosques and religious schools - which are off-limits for air strikes - days before seizing the city, said officials.

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Most of Marawi's 200,000 residents have fled the conflict and sought shelter at evacuation centres

Military spokesman Lt Col Jo-ar Herrera told AFP news agency that these buildings contained at least a month's worth of food, as well as weapons such as machine guns.

The gunman had also collected ammunition and provisions from the city after ransacking Marawi's jail and armouries, said presidential spokesman Ernesto Abella who was quoted in The Philippine Inquirer.

When the conflict first broke out, officials had said fighters from the Maute group, linked to the so-called Islamic State, stormed the city after an attempt by Philippine troops to capture Hapilon.

The Maute group is named after founders and leaders Abdullah and Omar Maute.